2021-01-01 11:28:10 +00:00
<!DOCTYPE HTML>
< html lang = "en" class = "sidebar-visible no-js rust" >
< head >
<!-- Book generated using mdBook -->
< meta charset = "UTF-8" >
< title > Iterating over an Option - Rust Design Patterns< / title >
<!-- Custom HTML head -->
< meta content = "text/html; charset=utf-8" http-equiv = "Content-Type" >
< meta name = "description" content = "A catalogue of Rust design patterns, anti-patterns and idioms" >
< meta name = "viewport" content = "width=device-width, initial-scale=1" >
< meta name = "theme-color" content = "#ffffff" / >
2022-01-17 20:53:51 +00:00
< link rel = "icon" href = "../favicon.svg" >
< link rel = "shortcut icon" href = "../favicon.png" >
< link rel = "stylesheet" href = "../css/variables.css" >
2021-01-01 11:28:10 +00:00
< link rel = "stylesheet" href = "../css/general.css" >
< link rel = "stylesheet" href = "../css/chrome.css" >
2022-01-17 20:53:51 +00:00
< link rel = "stylesheet" href = "../css/print.css" media = "print" >
2021-01-01 11:28:10 +00:00
<!-- Fonts -->
< link rel = "stylesheet" href = "../FontAwesome/css/font-awesome.css" >
2022-01-17 20:53:51 +00:00
< link rel = "stylesheet" href = "../fonts/fonts.css" >
2021-01-01 11:28:10 +00:00
<!-- Highlight.js Stylesheets -->
< link rel = "stylesheet" href = "../highlight.css" >
< link rel = "stylesheet" href = "../tomorrow-night.css" >
< link rel = "stylesheet" href = "../ayu-highlight.css" >
<!-- Custom theme stylesheets -->
2022-01-17 20:53:51 +00:00
< / head >
2021-01-01 11:28:10 +00:00
< body >
<!-- Provide site root to javascript -->
< script type = "text/javascript" >
var path_to_root = "../";
var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "navy" : "rust";
< / script >
<!-- Work around some values being stored in localStorage wrapped in quotes -->
< script type = "text/javascript" >
try {
var theme = localStorage.getItem('mdbook-theme');
var sidebar = localStorage.getItem('mdbook-sidebar');
if (theme.startsWith('"') & & theme.endsWith('"')) {
localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
}
if (sidebar.startsWith('"') & & sidebar.endsWith('"')) {
localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
}
} catch (e) { }
< / script >
<!-- Set the theme before any content is loaded, prevents flash -->
< script type = "text/javascript" >
var theme;
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
if (theme === null || theme === undefined) { theme = default_theme; }
var html = document.querySelector('html');
html.classList.remove('no-js')
html.classList.remove('rust')
html.classList.add(theme);
html.classList.add('js');
< / script >
<!-- Hide / unhide sidebar before it is displayed -->
< script type = "text/javascript" >
var html = document.querySelector('html');
var sidebar = 'hidden';
if (document.body.clientWidth >= 1080) {
try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
sidebar = sidebar || 'visible';
}
html.classList.remove('sidebar-visible');
html.classList.add("sidebar-" + sidebar);
< / script >
< nav id = "sidebar" class = "sidebar" aria-label = "Table of contents" >
< div class = "sidebar-scrollbox" >
2022-01-17 20:53:51 +00:00
< ol class = "chapter" > < li class = "chapter-item expanded " > < a href = "../intro.html" > < strong aria-hidden = "true" > 1.< / strong > Introduction< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../translations.html" > < strong aria-hidden = "true" > 1.1.< / strong > Translations< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/index.html" > < strong aria-hidden = "true" > 2.< / strong > Idioms< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../idioms/coercion-arguments.html" > < strong aria-hidden = "true" > 2.1.< / strong > Use borrowed types for arguments< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/concat-format.html" > < strong aria-hidden = "true" > 2.2.< / strong > Concatenating Strings with format!< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/ctor.html" > < strong aria-hidden = "true" > 2.3.< / strong > Constructor< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/default.html" > < strong aria-hidden = "true" > 2.4.< / strong > The Default Trait< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/deref.html" > < strong aria-hidden = "true" > 2.5.< / strong > Collections Are Smart Pointers< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/dtor-finally.html" > < strong aria-hidden = "true" > 2.6.< / strong > Finalisation in Destructors< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/mem-replace.html" > < strong aria-hidden = "true" > 2.7.< / strong > mem::{take(), replace()}< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/on-stack-dyn-dispatch.html" > < strong aria-hidden = "true" > 2.8.< / strong > On-Stack Dynamic Dispatch< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/ffi/intro.html" > < strong aria-hidden = "true" > 2.9.< / strong > Foreign function interface (FFI)< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../idioms/ffi/errors.html" > < strong aria-hidden = "true" > 2.9.1.< / strong > Idiomatic Errors< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/ffi/accepting-strings.html" > < strong aria-hidden = "true" > 2.9.2.< / strong > Accepting Strings< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/ffi/passing-strings.html" > < strong aria-hidden = "true" > 2.9.3.< / strong > Passing Strings< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/option-iter.html" class = "active" > < strong aria-hidden = "true" > 2.10.< / strong > Iterating over an Option< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/pass-var-to-closure.html" > < strong aria-hidden = "true" > 2.11.< / strong > Pass Variables to Closure< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/priv-extend.html" > < strong aria-hidden = "true" > 2.12.< / strong > Privacy For Extensibility< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/rustdoc-init.html" > < strong aria-hidden = "true" > 2.13.< / strong > Easy doc initialization< / a > < / li > < li class = "chapter-item expanded " > < a href = "../idioms/temporary-mutability.html" > < strong aria-hidden = "true" > 2.14.< / strong > Temporary mutability< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../patterns/index.html" > < strong aria-hidden = "true" > 3.< / strong > Design Patterns< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../patterns/behavioural/intro.html" > < strong aria-hidden = "true" > 3.1.< / strong > Behavioural< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../patterns/behavioural/command.html" > < strong aria-hidden = "true" > 3.1.1.< / strong > Command< / a > < / li > < li class = "chapter-item expanded " > < a href = "../patterns/behavioural/interpreter.html" > < strong aria-hidden = "true" > 3.1.2.< / strong > Interpreter< / a > < / li > < li class = "chapter-item expanded " > < a href = "../patterns/behavioural/newtype.html" > < strong aria-hidden = "true" > 3.1.3.< / strong > Newtype< / a > < / li > < li class = "chapter-item expanded " > < a href = "../patterns/behavioural/RAII.html" > < strong aria-hidden = "true" > 3.1.4.< / strong > RAII Guards< / a > < / li > < li class = "chapter-item expanded " > < a href = "../patterns/behavioural/strategy.html" > < strong aria-hidden = "true" > 3.1.5.< / strong > Strategy< / a > < / li > < li class = "chapter-it
< / div >
2021-01-01 11:28:10 +00:00
< div id = "sidebar-resize-handle" class = "sidebar-resize-handle" > < / div >
< / nav >
< div id = "page-wrapper" class = "page-wrapper" >
< div class = "page" >
< div id = "menu-bar-hover-placeholder" > < / div >
< div id = "menu-bar" class = "menu-bar sticky bordered" >
< div class = "left-buttons" >
< button id = "sidebar-toggle" class = "icon-button" type = "button" title = "Toggle Table of Contents" aria-label = "Toggle Table of Contents" aria-controls = "sidebar" >
< i class = "fa fa-bars" > < / i >
< / button >
< button id = "theme-toggle" class = "icon-button" type = "button" title = "Change theme" aria-label = "Change theme" aria-haspopup = "true" aria-expanded = "false" aria-controls = "theme-list" >
< i class = "fa fa-paint-brush" > < / i >
< / button >
< ul id = "theme-list" class = "theme-popup" aria-label = "Themes" role = "menu" >
< li role = "none" > < button role = "menuitem" class = "theme" id = "light" > Light< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "rust" > Rust (default)< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "coal" > Coal< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "navy" > Navy< / button > < / li >
< li role = "none" > < button role = "menuitem" class = "theme" id = "ayu" > Ayu< / button > < / li >
< / ul >
2022-01-17 20:53:51 +00:00
< button id = "search-toggle" class = "icon-button" type = "button" title = "Search. (Shortkey: s)" aria-label = "Toggle Searchbar" aria-expanded = "false" aria-keyshortcuts = "S" aria-controls = "searchbar" >
2021-01-01 11:28:10 +00:00
< i class = "fa fa-search" > < / i >
< / button >
2022-01-17 20:53:51 +00:00
< / div >
2021-01-01 11:28:10 +00:00
< h1 class = "menu-title" > Rust Design Patterns< / h1 >
< div class = "right-buttons" >
2022-01-17 20:53:51 +00:00
< a href = "../print.html" title = "Print this book" aria-label = "Print this book" >
2021-01-01 11:28:10 +00:00
< i id = "print-button" class = "fa fa-print" > < / i >
< / a >
2022-01-17 20:53:51 +00:00
< a href = "https://github.com/rust-unofficial/patterns" title = "Git repository" aria-label = "Git repository" >
2021-01-01 11:28:10 +00:00
< i id = "git-repository-button" class = "fa fa-github" > < / i >
< / a >
< / div >
< / div >
2022-01-17 20:53:51 +00:00
< div id = "search-wrapper" class = "hidden" >
2021-01-01 11:28:10 +00:00
< form id = "searchbar-outer" class = "searchbar-outer" >
2021-05-14 04:50:28 +00:00
< input type = "search" id = "searchbar" name = "searchbar" placeholder = "Search this book ..." aria-controls = "searchresults-outer" aria-describedby = "searchresults-header" >
2021-01-01 11:28:10 +00:00
< / form >
< div id = "searchresults-outer" class = "searchresults-outer hidden" >
< div id = "searchresults-header" class = "searchresults-header" > < / div >
< ul id = "searchresults" >
< / ul >
< / div >
< / div >
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
< script type = "text/javascript" >
document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
});
< / script >
< div id = "content" class = "content" >
< main >
2021-03-02 21:12:13 +00:00
< h1 id = "iterating-over-an-option" > < a class = "header" href = "#iterating-over-an-option" > Iterating over an < code > Option< / code > < / a > < / h1 >
< h2 id = "description" > < a class = "header" href = "#description" > Description< / a > < / h2 >
2021-01-21 23:00:21 +00:00
< p > < code > Option< / code > can be viewed as a container that contains either zero or one
2021-08-25 02:43:39 +00:00
element. In particular, it implements the < code > IntoIterator< / code > trait, and as such
2021-01-21 23:00:21 +00:00
can be used with generic code that needs such a type.< / p >
2021-03-02 21:12:13 +00:00
< h2 id = "examples" > < a class = "header" href = "#examples" > Examples< / a > < / h2 >
2021-01-21 23:00:21 +00:00
< p > Since < code > Option< / code > implements < code > IntoIterator< / code > , it can be used as an argument to
< a href = "https://doc.rust-lang.org/std/iter/trait.Extend.html#tymethod.extend" > < code > .extend()< / code > < / a > :< / p >
2021-01-01 11:28:10 +00:00
< pre > < pre class = "playground" > < code class = "language-rust edition2018" >
< span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > let turing = Some(" Turing" );
let mut logicians = vec![" Curry" , " Kleene" , " Markov" ];
logicians.extend(turing);
// equivalent to
if let Some(turing_inner) = turing {
logicians.push(turing_inner);
}
< span class = "boring" > }
< / span > < / code > < / pre > < / pre >
2021-01-21 23:00:21 +00:00
< p > If you need to tack an < code > Option< / code > to the end of an existing iterator, you can
pass it to < a href = "https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.chain" > < code > .chain()< / code > < / a > :< / p >
2021-01-01 11:28:10 +00:00
< pre > < pre class = "playground" > < code class = "language-rust edition2018" >
< span class = "boring" > #![allow(unused)]
< / span > < span class = "boring" > fn main() {
< / span > let turing = Some(" Turing" );
let logicians = vec![" Curry" , " Kleene" , " Markov" ];
for logician in logicians.iter().chain(turing.iter()) {
println!(" {} is a logician" , logician);
}
< span class = "boring" > }
< / span > < / code > < / pre > < / pre >
2021-01-21 23:00:21 +00:00
< p > Note that if the < code > Option< / code > is always < code > Some< / code > , then it is more idiomatic to use
< a href = "https://doc.rust-lang.org/std/iter/fn.once.html" > < code > std::iter::once< / code > < / a > on the
element instead.< / p >
< p > Also, since < code > Option< / code > implements < code > IntoIterator< / code > , it's possible to iterate over
it using a < code > for< / code > loop. This is equivalent to matching it with < code > if let Some(..)< / code > ,
and in most cases you should prefer the latter.< / p >
2021-03-02 21:12:13 +00:00
< h2 id = "see-also" > < a class = "header" href = "#see-also" > See also< / a > < / h2 >
2021-01-01 11:28:10 +00:00
< ul >
< li >
2021-01-21 23:00:21 +00:00
< p > < a href = "https://doc.rust-lang.org/std/iter/fn.once.html" > < code > std::iter::once< / code > < / a > is an
iterator which yields exactly one element. It's a more readable alternative to
< code > Some(foo).into_iter()< / code > .< / p >
2021-01-01 11:28:10 +00:00
< / li >
< li >
2021-01-21 23:00:21 +00:00
< p > < a href = "https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.filter_map" > < code > Iterator::filter_map< / code > < / a >
is a version of < a href = "https://doc.rust-lang.org/std/iter/trait.Iterator.html#method.flat_map" > < code > Iterator::flat_map< / code > < / a > ,
specialized to mapping functions which return < code > Option< / code > .< / p >
2021-01-01 11:28:10 +00:00
< / li >
< li >
2021-01-21 23:00:21 +00:00
< p > The < a href = "https://crates.io/crates/ref_slice" > < code > ref_slice< / code > < / a > crate provides functions
for converting an < code > Option< / code > to a zero- or one-element slice.< / p >
2021-01-01 11:28:10 +00:00
< / li >
< li >
< p > < a href = "https://doc.rust-lang.org/std/option/enum.Option.html" > Documentation for < code > Option< T> < / code > < / a > < / p >
< / li >
< / ul >
< / main >
< nav class = "nav-wrapper" aria-label = "Page navigation" >
<!-- Mobile navigation buttons -->
2022-01-17 20:53:51 +00:00
< a rel = "prev" href = "../idioms/ffi/passing-strings.html" class = "mobile-nav-chapters previous" title = "Previous chapter" aria-label = "Previous chapter" aria-keyshortcuts = "Left" >
2021-01-01 11:28:10 +00:00
< i class = "fa fa-angle-left" > < / i >
< / a >
2022-01-17 20:53:51 +00:00
< a rel = "next" href = "../idioms/pass-var-to-closure.html" class = "mobile-nav-chapters next" title = "Next chapter" aria-label = "Next chapter" aria-keyshortcuts = "Right" >
2021-01-01 11:28:10 +00:00
< i class = "fa fa-angle-right" > < / i >
< / a >
< div style = "clear: both" > < / div >
< / nav >
< / div >
< / div >
< nav class = "nav-wide-wrapper" aria-label = "Page navigation" >
2022-01-17 20:53:51 +00:00
< a rel = "prev" href = "../idioms/ffi/passing-strings.html" class = "nav-chapters previous" title = "Previous chapter" aria-label = "Previous chapter" aria-keyshortcuts = "Left" >
2021-01-01 11:28:10 +00:00
< i class = "fa fa-angle-left" > < / i >
< / a >
2022-01-17 20:53:51 +00:00
< a rel = "next" href = "../idioms/pass-var-to-closure.html" class = "nav-chapters next" title = "Next chapter" aria-label = "Next chapter" aria-keyshortcuts = "Right" >
2021-01-01 11:28:10 +00:00
< i class = "fa fa-angle-right" > < / i >
< / a >
2022-01-17 20:53:51 +00:00
< / nav >
2021-01-01 11:28:10 +00:00
< / div >
2022-01-17 20:53:51 +00:00
< script type = "text/javascript" >
2021-01-01 11:28:10 +00:00
window.playground_copyable = true;
< / script >
2022-01-17 20:53:51 +00:00
< script src = "../elasticlunr.min.js" type = "text/javascript" charset = "utf-8" > < / script >
2021-01-01 11:28:10 +00:00
< script src = "../mark.min.js" type = "text/javascript" charset = "utf-8" > < / script >
< script src = "../searcher.js" type = "text/javascript" charset = "utf-8" > < / script >
< script src = "../clipboard.min.js" type = "text/javascript" charset = "utf-8" > < / script >
< script src = "../highlight.js" type = "text/javascript" charset = "utf-8" > < / script >
< script src = "../book.js" type = "text/javascript" charset = "utf-8" > < / script >
<!-- Custom JS scripts -->
< / body >
< / html >
